2i6 • ALUS. [Vol. XVIII. 



interarcualis of the fifth arch, the small posterior bundle of the 

 transversus dorsalis posterior, and the longitudinal muscle fibers 

 that extend forward between the two fifth ceratobranchials, all 

 belong to this class. In addition to these muscles there is a broad, 

 flat muscle-bundle inserted along the posterior edge of the proxi- 

 mal articular head of the fourth epibranchial, and a broad and 

 important longitudinal prolongation between the posterior dorsal 

 pharyngeal bones. The former muscle, which is only differentiated 

 from the constrictor cesophagei on the dorsal surface of the 

 oesophagus, is continuous, along its entire lateral edge, with the 

 so-called interarcualis of the fifth arch. The longitudinal anterior 

 prolongation of the constrictor runs forward between and ventral 

 to the retractores arcuum branchialium dorsales, and ventral to the 

 transversus dorsalis posterior. It is inserted, in part, along the 

 mesial edge of each pharyngeal bone, and in part it continues for- 

 ward between those bones as a thin layer of longitudinal fibers 

 which gradually disappear. 



ThePharyngo-Claviculares andPharyngo-Hyoideus form, 

 on each side of the head, a group of three flat muscles inserted 

 along the ventral edge of the ventral process or wing of the fifth 

 ceratobranchial. All three pull the pharyngeal bone downward; 

 the hyoideus pulling it downward and forward, the claviculares 

 downward and backward. 



The pharyngo-hyoideus [Ph) is the anterior and external mus- 

 cle of the group. It arises from the dorsal edge of the posterior 

 part of the sternum, runs upward and backward, and is inserted 

 along the anterior half of the ventral edge of the ventral wing of 

 the fifth ceratobranchial. It is tendinous both at its origin and at 

 its insertion, and is crossed, not far from its origin, by a narrow 

 tendinous line .which extends entirely through the muscle. Directly 

 internal to, and in contact with this tendinous line the truncus 

 arteriosus runs forward and slightly upward. About half way 

 between this tendinous line and the upper end of the muscle there 

 is a tendinous patch on the external surface of the muscle. The 

 muscle either pulls the pharyngeal bone downward and forward, 

 or the sternum upward and backward. Its innervation could not 

 be satisfactorily determined, but it seemed to be by a branch of the 

 ramus posttrematicus of the second vagus. A delicate terminal 



